Instead security assurances to Ukraine (Ukraine published the documents as guarantees given to Ukraine[5]) were given on 5 December 1994 at a formal ceremony in Budapest (known as the Budapest Memorandum on Security Assurances[6]), may be summarized as follows: Russia, the UK and the USA undertake to respect Ukraine's borders in accordance with the principles of the 1975 CSCE Final Act, to abstain from the use or threat of force against Ukraine, to support Ukraine where an attempt is made to place pressure on it by economic coercion, and to bring any incident of aggression by a nuclear power before the UN Security Council.
In other words, no guaranties and only the most tepid of assurances.
The Sink Emperor wasn't called "Slick Willy" only for his slimy sexual proclivities.
The guarantee is still there, but due to the lack of ratification it is not enforceable by us.
Obviously Obama is not going to do anything. Putin wins the game of chicken easily, and I still think Putin is himself a coward.
The fact remains that for Russia (some abstract, non-existent “Russia”), to claim Crimea back the RF needs to renounce its succession from the USSR and go back to the law system of the Russian Empire. Which I would heartily welcome.